Self-adhering friction reducing liner and method of use

ABSTRACT

A patch of low friction materials, such as a film of polytetrafluoroethylene is sized to provide an area of low friction support for a portion of a human body relative to an object such as a shoe or prosthetic socket. The patch can be lined with foam, or preferably, a stretch fabric so that it will fit around irregular contours of the shoe, or socket, or the skin itself. The patches reduce shear trauma in critical load areas. After identifying regions of high loads, the method comprises applying the patches as needed to avoid sores, calluses, blisters and abrasions.

BACKGROUND OF THE INVENTION

The present invention relates to the use of very low friction materialformed into patches or pieces and adhered to the skin or to a surface incontact with the skin (or immediately adjacent material such as a sock)to lower the magnitude of tangential traction of the surface in contactwith the skin. The material reduces the likelihood of abrasion, traumaand ulceration in localized areas.

In the prior art, there have been efforts to reduce the co-efficient offriction of materials in load bearing contact with the skin, such as thesurface of a lining of a shoe, which slides against a stocking. Also theregions where a limb prosthesis is in load bearing contact with aresidual limb have been extensively considered for ways of reducingproblems. The co-efficient of friction of smooth leather varies,depending on the moisture content, and when it gets wet can be quitehigh in friction. Moleskin patches have been sold and used for coveringcorns on the feet, as well as covering calluses, but this also has arelatively high co-efficient of friction against the inner surface of ashoe and the co-efficient of friction increases substantially when themoleskin is wet.

Blisters, abrasions, calluses, bursas and even some forms ofsub-cutaneous tissue trauma are the result of applications of acombination of forceful contact and tangential tractions to the skin(forceful rubbing/forceful shearing). High shear stresses may causedamage in a single cycle. Low shear stresses may cause tissue damagewhen the number of cycles is great.

Tangential skin tractions relate directly to tissue shear stress andshear strain magnitudes. Shear strain is by its very nature verydistortional and, when it exceeds certain levels, results in the tearingof biological tissues such as blood capillaries and interface(skin-subcutaneous) layers. High normal pressures (perpendicular to theskin surface) in the absence of significant tangential tractions aresurprisingly well tolerated by skin and underlying tissue, especiallywhen applications are of a short enough duration to avoid ischemictrauma (cell death after an extended period of blood flow blockage).

This invention is primarily aimed at reducing and preventing sheartrauma from many repetitions of short duration skin loadings, buteliminating shear tractions even in low repetition, long-durationloadings is of value. Research shows that even capillary blood flow isaffected strongly by whether or not shear stresses are superimposed onnormal pressures. When high shear stresses are present, capillary bloodflow has been shown to be occluded at normal pressures only half asgreat as what are required to occlude flow in the absence of shearstresses and strains.

There is some recognition among medical researchers and care-givers thatshear plays a role in tissue trauma. However, how and when excessiveshear stresses/strains occur and how they damage tissue are hard tovisualize. Injury from a normal force (a simple, yet forceful, blow orbump causing injury by crushing tissue) is easier for people tovisualize and understand. Shear stresses and how they vary over a givenarea (and vary with time) are very hard to measure; much harder than itis to measure normal pressure. In addition to the visualization andmeasurement difficulties just mentioned, there is the fact that fewpeople have better than a vague qualitative awareness of how somethingcalled the “coefficient of friction” (C.F.) relates to blisters,abrasions, and calluses. Tangential traction force magnitudes can be nogreater than the C.F. times the magnitude of normal force. Therefore,the simplest, most direct way to reduce shear induced tissue trauma isto choose materials which minimize friction against the at-risk skinsurface areas. Until the present invention, there has been littlepractical awareness of, and attention given to, friction management.

Examination and knowledge of products on the market indicate that theopportunities for reducing callusing, blistering and abrasions byfriction management has been almost entirely unappreciated by designersof shoes, orthoses, prostheses, and many other objects that come inrepeated or prolonged contact with the human body.

Thin silk or synthetic fiber sheets have been used by amputees to pullover their residual limbs before pulling on a cotton or wool sock andthen donning the limb prosthesis. The co-efficient of friction betweenthe sheet and the sock is reduced under dry conditions and does protectthe residual limb to some extent from friction and consequentshear-related trauma. The coefficient of friction increasessubstantially when the material becomes damp or wet. In most cases, thematerial used to line shoes and prosthesis sockets, for example,represent high friction choices. Foam products are used to lineprosthetic sockets, orthoses, and shoe insoles and represent aparticularly poor material from the standpoint of friction management.Damp skin and sock material literally sticks to such foams.

Synthetic gel socket liners are available, and these are generally inthe range of ⅛ to 5/16 inch thick. The liner cover tends to stick to theskin and other materials in contact with it, so that it does not act asa friction reducer, but does provide cushioning and accommodates smallamplitude shear motions without much resistance. The effectiveness of agel liner is dependent on its thickness, and as it becomes thicker, itsweight and bulk are deterrents.

Thus, the concept of providing a very low friction interface between theskin and surfaces that contact the skin, particularly in high load andhigh shear areas, has escaped the workers in the field and the needexists for reduction of trauma to the skin where the skin and tissue aresupported.

SUMMARY OF THE INVENTION

The present invention relates to providing a layer of material that hasa very low friction outer surface in both dry and wet conditions toprovide an interface with a surface that normally would support the skineither directly or through a cloth covering, such as a sock fabric. Inthe usual situation, the surface loading or bearing on the skin may bethe inner surface of an orthosis, the socket surface of a prosthesis, orinner surfaces of a shoe, especially insoles, but also other innersurfaces. The layer of low-friction material is adhered, preferably, tothe surface of the object that bears on the skin and faces the skin,although applying the layer with an adhesive directly on the skin in theaffected area with the low friction surface facing the support is alsocontemplated. The purpose of the low friction material is to lower themagnitude of tangential tractions that the surface of the object canexert against the skin.

The use of intervening layers is contemplated in the present invention,so a sock or sheet placed between the low friction pad and the skin doesnot adversely affect the performance.

A low friction surface layer used may be on material in the form of asheet, or a small patch that is pre-cut, or custom cut to a desiredsize, and having a pressure sensitive adhesive on the surface of thepatch opposite from the low friction surface. The adhesive may be on theouter surface of another layer of material, such as a foam backingcushion layer or a stretch fabric backing bonded to the low frictionmaterial. A release paper is placed on the exposed adhesive. When therelease paper is removed, the patch or piece of material providing thelow friction surface layer can be adhered into a certain desiredposition of the surface of the skin or on the object that bears on theskin.

Preferably, the low friction layer is a thin film material having thesurface friction characteristics of polytetrafluoroethylene (PTFE) ThePTFE layer is preferably bonded to a fabric layer of a somewhat elastic,flexible material such as Lycra or a Lycra blend. The exposed side ofthe fabric is covered with a pressure adhesive and a release paper is ontop of the adhesive.

The thin sheet of PTFE material can be used without any backing sheetsby applying adhesive directly to the PTFE layer. Bonding a very thinsheet of PTFE to a stretch fabric without having the PTFE separate fromthe fabric during use gives the desired low friction characteristics ofthe outer surface, while permitting the formed patch to conform toirregular shapes or surfaces, because of the stretch fabric underneaththe thin layer of PTFE. The stretch fabric also gives the thin layer oflow friction material, such as PTFE, “body” so it can be handledreasonably during the release paper stripping and application of thelayer or patch to the desired surface. Very thin layers of PTFE tend towrinkle or fold and cause problems with getting them very smooth. Theelasticity of the backing fabric allows conformance into recesses, overconvexities, and onto a combination of compound contoured surfaces.

Cushioning material, such as foam can be placed between the patch andthe surface supporting the patch, if desired, to provide a cushioningeffect, as is known. Various shapes can be made, including shapes whichwould have the stretch fabric toward the center of the patch or piece sothat it was surrounded by an adhesive coated thin low friction material.

A preferred method of use includes placement of suitable size pieces orpatches of the low friction coefficient material either on the skin oron the surface that will be next to the skin in locations where sheartrauma is likely to occur. These patches or pieces can be held in placewith suitable adhesive on the back side of the low friction material.Foam or other compressible material for cushioning can be used whereverneeded.

Another aspect or form of the protective patch is the PTFE film or layerbonded to a calf skin leather hide, textile foam liner, or othermaterial that could be used to line the inner wall of the toe box of ashoe. The composite material can be sewn and applied in the same manneras the lining material now is applied without a PTFE film surface. Theusefulness of this material is realized in its ability to shield dorsaland peripheral surfaces of the foot from damaging shear forces. At thesenon-plantar locations, high tangential tractions can be present, butmore often trauma develops from lower forces, that generate excessivecallus/corn growth and/or tissue breakdown by the action of cyclic (highfrequency) loading.

The patches of the present invention offers an easy way to accomplish“friction management”. The surfaces that a shoe, orthosis, or prosthesispresent to the skin vary as to their function and as to the tissuetrauma risk they present. It is also true that some areas of the anatomywithin a shoe, prosthesis, or orthoses are at greater or lesser riskbecause of the level of peak forces and/or the amount of soft tissueinterposed between skin and bone. Some parts of an orthosis bear onlyslightly or not at all against the corresponding skin surface. Otherparts bear very firmly in order to provide maximum orthopedic support,correction, or weight bearing. Still other surfaces such as thesupra-condylar parts of a BK (lower leg) prosthesis socket serve tosuspend (during swing-through) or maintain position of the device.

All of these just-noted facts are important because they are reasons tovary the friction coefficient depending on the surface function. Forinstance, there is very little reason to be concerned about the frictioncoefficient of a surface in only very light contact with the skin(unless the number of repetitions is very high). Forceful cyclicalcontact against a skin surface is a situation that benefits more fromminimizing the friction coefficient. If the area is “bony” minimizingfriction becomes more important.

In a case like the supra-condylar suspension areas of the BK socketmentioned earlier, high friction (even “sticky”) materials may bedesired. Applying the low friction patches of an aspect of the inventionto certain areas and not others is a way to add friction management tothe orthotist's (prosthetist's, podiatrist's, etc.) treatment methodsand appliances. In cases where the professional wishes to apply maximumsupportive/corrective pressure the near elimination of friction andshear in selected regions means that much greater support can be safelyprovided without approaching tissue trauma conditions.

There are also many consumer (non-professional) applications for thepresent invention. Many people are plagued by excessive callus build-up.A person with excessive calluses under the metatarsal heads might removethe shoe insoles and apply low friction patches to the correspondingsurface of the insole. If the excessive callus is in the form of“corns”, the person could apply a low friction corn pad to relieve somepressure on a painful corn (by means of annular cushioning material) andgreatly reduce the friction and shear which originally generated, andthen maintains the corn callus.

A similar but much larger patch might be applied by a skater over anklebones to allow tight(er) lacing with greater comfort and less chance oftrauma at the apices of those bony prominences. As an alternative, theskater may choose to adhere the patch to the appropriate locations onthe inside surface of the skate uppers. There are a myriad of otherpossibilities such as on kneeling pads (for cement workers, etc.) or onbackpack shoulder straps.

A similar (but non-consumer) use of the cushioned patch (continuous,annular, or donut types) is in hospitals for prevention of bed sores.Low friction cushion patches of the present invention applied overhealthy bony areas such as sacrum-coccyx, greater trochanter, heels, andelbows as a prophylactic measure act to inhibit the generation of bedsores.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a layer of material made with a low frictionsurface material according to the present invention;

FIG. 2 is a sectional view taken on line 2-2 in FIG. 1 showing thelayers used;

FIG. 3 is a plan view of a form of patch;

FIG. 4 is a sectional view of a patch made according to an aspect of thepresent invention, taken on line 4-4 in FIG. 3 including a layer of lowfriction material that will lower friction loads on the skin in aselected area;

FIG. 5 is a cross sectional view of a modified aspect of the presentinvention;

FIG. 6 is a plan view of a further modified patch made according to thepresent invention;

FIG. 7 is a sectional view taken on line 7-7 in FIG. 6;

FIG. 8 is a plan view of a further modified patch made according to thepresent invention;

FIG. 9 is a sectional view of the patch shown in FIG. 8 taken on line9-9 in FIG. 8;

FIG. 10 is a schematic representation of a typical shoe showing regionshaving patches made according to the present invention installed forreducing shear damage to tissue;

FIG. 11 is a perspective view of an ankle and foot orthosis showinglocations where patches having a low friction surface according to thepresent invention are installed, and which can be installed either onthe orthosis as shown, or as shown in FIG. 12 on a foot on which theorthosis will be worn;

FIG. 12 is a schematic showing of a foot and ankle indicating desiredlocations of low friction patches for an orthosis;

FIG. 13 is a top plan view of a prosthetic socket for a lower legprosthesis showing regions on the interior of the socket where lowfriction pads would be installed to reduce tissue trauma caused byshear;

FIG. 14 is a schematic representation of a leg and knee that would fitinto the prosthesis of FIG. 13, and showing locations of low frictionpatches made according to the present invention;

FIG. 15 is a perspective view of a longer leg prosthetic device having asocket for receiving the upper portion of a leg to which the prosthesiswould be attached and illustrates locations of low friction patches madeaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate a simple form of the invention which includes acomposite sheet 10 made in a suitable size, which can be used forcutting individual interface patches or pieces from the sheet. Thecomposite sheet 10 includes a thin film or layer 12 ofpolytetrafluoroethylene (PTFE). Layer 12 is preferably bonded to astretch fabric layer 14, such as Lycra or stretch nylon, which also isrelatively thin. The top layer of PTFE can be in the range of 2.5 milsthick, and the layer of fabric 14 could be slightly thicker than that,as needed to make a suitable stretch weave. The PTFE film 12 isconformable and will stretch, so that the stretch fabric will cause thePTFE layer to move with it, if it is stretched in any direction. A thinlayer of adhesive 16 is shown in the drawings on an opposite side orsurface of fabric layer 14 from the PTFE layer 12. A suitable releasepaper 18 is provided over the adhesive on the fabric.

The sheet 10 can be used for cutting out various configuration, such asthose shown in dotted lines at 20, for custom fitting patches of the lowfriction material 12. It can be seen that the low friction material film12 has an upper surface 13 which faces, and supports the skin. Also asshown schematically perforations 15 can be provided for breathability ofthe patch. When the patch such as that shown by dotted lines 20 isplaced on the skin, for an interface with a shoe, prosthesis, ororthosis, as desired the surface 13 faces away from the skin. Thepurpose of applying the patch is to lower the magnitude of tangentialtraction that the surface of loan object worn by a person can exertagainst the skin. The PTFE film is bonded to one surface of the fabriclayer, and is available from Chemfab Corporation of Merrimack, N.H.,USA.

The sheet 10 is usable in large areas, or can be cut for small areas asdesired. Premanufactured special size and shape patches or pieces can bemade, as shown in FIG. 3 where a patch 26 is illustrated in generally arectangular configuration. An exploded section of the patch 26 is shownin FIG. 4, except that in FIG. 3 the release paper is shown removed toprovide a view of a foam layer 30 around which the adhesive layer 32extends. The sectional views are shown exploded, for illustration butthe layers are bonded together in use.

The patch 26 comprises a film or layer 28 of the low friction material,such as PTFE, bonded to a plastic foam layer 30 that is of smaller sizethan the PTFE film layer. The foam 30 is shown in FIG. 4 to besubstantially thicker than the PTFE film layer, but it can be anythickness desired. The pressure sensitive adhesive layer 32 is thenapplied, and can be provided only on the peripheral edges as shown inFIG. 3, to provide an open center where the foam layer 30 would beexposed for contact with the skin. A release paper layer 34 overlies thebottom of the patch. The exterior surface 29 of the PTFE film layer 28provides the low friction surface for reducing shear and tangentialtraction against a support surface or material. The foam layer 30 may bein contact with the skin or the surface of the support to providecushioning and protection. The foam layer 30 could be, for example, inthe range of a quarter inch thick, but would have tapered or skivededges as shown so that the PTFE film layer 28 would conform well to thefoam. The adhesive used is selected to bond to the PTFE layer so thereis an adhesive edge for adhering the patch on the skin or other surface.The adhesive is a pressure sensitive adhesive.

The preformed patch 26 shown in FIG. 3 can be sized to be 2, 3, or 4inches long, for example, with widths of 1, ½ and 2 inches. The patch 26thus can be used for any application where a spot or region of skin issubject to shear and abrasion, so the tissue is becoming tender, torelieve the tangential traction on that portion of the skin.

FIG. 5 illustrates an exploded cross section of a modified patch 36having the periphery shown in FIG. 3. The patch 36 has a PTFE film layer38. The PTFE film layer 38 is bonded to a stretch fabric layer 40 suchas stretch nylon or Lycra. A foam layer 42 is bonded to the fabric layer40 in the center portions of the patch. The pressure sensitive adhesivelayer 44 is placed on the surface of the fabric layer opposite from thelow friction outer surface 39 of PTFE film layer 38. The adhesive layer44 again can be formed as shown in FIG. 3 with a rim of adhesivesurrounding an open center where the foam layer 42 is exposed. A releasepaper 46 is also provided on the patch as shown in cross section. Asstated, the PTFE films can be perforated as desired.

The use of the stretch fabric 40 provides an additional layer ofcushioning and protection, which can be stretched along with the PTFEfilm to fit rounded surfaces or irregularities. The foam layer 42 lohasits edges beveled, and the stretch fabric layer 40 and the PTFE filmlayer 38 will fit closely around the foam. The stretch fabric layer 40is bonded to the PTFE film layer 38 before placing the foam in position,so both the fabric and the PTFE would be stretched at the same time.This bonding, again, is done commercially by Chemfab Corporation ofMerrimack, N.H., USA. The PTFE film also can be bonded to leather andother fabrics by ChemFab Corporation.

Peripheral dimensions of the patches for the construction shown in FIG.5 can be the same as those shown in connection with FIG. 3, and thebottom view would be the same as well. Of course other configurationssuch as elliptical shapes and the like can be used. The pressuresensitive adhesive layer 44 can extend all the way across the foam, sothere is no open center, if desired.

In FIGS. 6 and 7 a modified form of the invention is shown, which haslow coefficient of friction film on both surfaces of the patch, so whenthe patch that is shown in FIG. 7 is placed on a corn or callus, thesurface in contact with the skin has the low coefficient of friction andthe outwardly facing surface does also. The patch 50, as shown iselliptically shaped, and in FIG. 7 a cross sectional exploded view isillustrated. A PTFE film layer having a low coefficient of frictionouter surface 53 is bonded to a stretch fabric layer 54 and then a foamlayer 56 that has a hole 57 through the center is provided in the centerportions of the patch 50. In this form of the invention, a layer 60 ofPTFE film that is relatively small in size is positioned in the hole 57in the foam and is bonded to the fabric layer for example with pressuresensitive adhesive. A pressure sensitive adhesive layer 58 is thenbonded to the stretch fabric layer 54 and the underside of the foamlayer 56 but surrounding the hole 57. A release paper layer 59 overliesthe bottom surface of patch 50 and over the adhesive. The layer of PTFEfilm 60 is shown in both FIGS. 6 and 7, and has an outwardly facing lowcoefficient of friction surface 61 that will reduce any abrasion of skinthat it contacts.

The foam layer 56 has a generally elliptically shaped periphery as shownin dotted lines in FIG. 6, and the overall configuration then would be apatch 50 that could be adhered to skin, to provide a low frictionmaterial directly against the skin with the small layer of film 60, anda larger area of low friction film defined by layer 52 that could engagethe lining of a shoe or the inner surface of a sock or the like.

FIGS. 8 and 9 illustrate a further modified form of the inventioncomprising an elliptically shaped piece or patch 66 that is made of alayer 68 of PTFE film having an outer low coefficient of frictionsurface 69. Layer 68 is bonded to a stretch fabric layer 70. A secondlayer of PTFE film 72, is smaller in size than the top PTFE film layer68 and the stretch fabric 70 and is bonded to the stretch fabric 70 inthe center portions of the patch on an opposite side of the fabric fromthe PTFE film layer 68. This can be seen in FIG. 8.

A layer of pressure sensitive adhesive 74 is then applied to theperipheral rim area surrounding the film layer 72, and will provide foran adhesive layer of sufficient size to permit adhering the patch 70 tothe skin, or objects or supports for the skin. A release paper layer 75is provided. This patch is made without any cushioning or foam layer.The smaller center layer 72 of PTFE film does not have any adhesivebetween it and the skin, so this is not adhered to the skin, but has alow friction surface 73 that is free to slide against the skin. Thisreduces the friction on the load carrying surfaces significantly, andreduces trauma from shear, even when it is of low magnitude. Lowmagnitude shear can cause tissue damage if it cycles repeatedly.

FIG. 10 illustrates schematically a foot within a shoe drawn in phantomto illustrate in cross section, regions where high load and/or rubbingareas can benefit from the application of the low friction patches madeaccording to the present invention. In FIG. 10, the bones of the footare illustrated at 80, and they are shown within the outline of a shoe82. High load bearing areas of course are located under the metatarsalheads 84, the heel or calcaneus 90, and the end of the toes, inparticular the big toe 97. The metatarsal heads 84 are supported on apatch 86. This patch 86 can be on top of the insole 87 and thus betweenthe sock (and foot) and the support provided by shoe 82. The patch 86can be installed in the shoe 82 permanently, by sewing if desired. Patch86 provides a low friction surface area where the sock can slide easilyrelative to the surface of the patch 86 and will not tend to abradeagainst the skin of the foot in the high load support area.

The patch or pad 86 can extend across the width of the metatarsals, sothat the entire metatarsal head region (the metatarsal-phalangeal jointregion) of the foot is supported on a relatively low friction surface.The patch or pad 86 preferably has an outer PTFE film layer, backed by astretch fabric and held in place on the shoe insole. A foam layer asshown in FIG. 5 can be provided in the patch or pad 86, if desired.

Another region that can be supported is at the toe end surfaces, inparticular the big toe, such as that shown with a pad 88 under end ofthe big toe 97. This is a region that is not subjected to extremely highloads, but there is a lot of cyclic loading, including shearing, as onemoves. The toe supports forces as the person pushes off on each stride,particularly when running.

The heel bone or calcaneus indicated at 90 has a bony prominence 92,that is supported on a patch 94 having a low coefficient of frictionouter surface region. The patch or pad 94 will provide support andreduce any shear loads if there is slippage during the stride.Additionally, the cushioning patches that are shown, having a foam layercan provide some cushioning support and conformability aroundprotrusions in the heel bone to reduce trauma and damage.

A non-load-bearing area where cyclic shear loads can cause damage isshown above a toe where a joint may be deformed or contracted so thebone is raised up as shown at 96 and will tend to rub against an uppersurface of the toe box 98 of the shoe 82. The installation of a pad 100directly on the toe, or on the interior of the shoe on the top interiorsurface of the toe box will reduce the shear loading to a point whereeven cyclical loading will not cause shear damage, blistering, callusingor the like. In a nonweight-bearing area, therefore, the low frictionsurface patches also provide relief. Bonding PTFE film to leatherpermits lining the toe box of a shoe to reduce friction in the entiretoe region.

The patches or pads of the present invention find needed application inankle-foot orthoses. One such orthosis is shown in FIG. 11, at 104 andincludes a foot support shell 106, and ankle and leg support shell 108joined together with flexure members 110 in a conventional manner sothat the foot shell 106 can be flexed relative to the leg support. Theshells are open in the front and top, as can be seen, and a retainingstrap 112 is used for retaining the leg in position. Additional securingdevices can be used for the foot.

The interior surfaces of the shells 106 and 108 support the foot, theankle, and the lower leg snugly, but there can be some sliding or shearforces generated. A patch 114 that is relatively large and which can becut from the form of the invention shown in FIG. 1, is positioned in thelongitudinal arch area. Suitable foams can be used between the shellsurface and the pad, a low friction material PTFE is provided on the topsurface of the patch that engages the underside of a foot in theorthosis, through a sock, in this high load support area. The pad orpatch 114 can be configured to provide support in the arch area as wellas reducing the friction loads that occur from any sliding, particularlyunder high forces. The patch 114 can be made as shown before with foamunderneath the PTFE film layer. Use of a stretch fabric layer backingthe PTFE film is desired because of some irregular contours that have tobe followed on the formed foot shell 106.

The low friction surface pads used where there is flexing, insures thatthe shear loads are very low, and have the advantage of having foamattached or bonded to the film surface. Conventional foam pads are veryhigh friction and will tend to cause tissue damage from repeated shearloads even though direct weight support is not present. Additionally, amedial leg support patch or pad shown at 120 can be provided above theankle bone, and this includes foam padding behind a PTFE film layer forincreasing or modifying the pressure distribution and provide increasedcorrective forces. The pad 120 can be again cut to the desired shape,and suitable foams can be used under the PTFE layer. Here, too, the padpreferably has the bonded stretch fabric beneath the outer PTFE filmlayer because of the need of conforming to irregular contours.

The edges of the shell can be lined with the low friction surfacepatches or pads 122 to reduce shear in these regions. The patches orpads can be folded over the edges and adhered in place. The main portionof the pads on the edges should be on the interior surfaces.

FIG. 12 illustrates a typical foot and lower ankle joint, and the regionshown at 114A, where the pad or patch 114 would bear on the arch. Theupper pad or patch region on the leg is shown at 120A.

FIG. 13 is a top view of a typical transtibial prosthetic leg 123. Theprosthetic leg 123 includes a rigid socket 124 and a soft socket liner125 which will receive a residual limb, and support the residual leg atand just below the knee. In such a prosthesis, there are regions wheretissue is thin over bony prominences, such as at the lateral, anteriorand bony prominences near the top of the tibia and the tibia crest.These regions are also shown in FIG. 13, and pads shown at 126 and 128for bony prominences are placed appropriately in the socket liner 125.The socket has a rigid shell 124 that normally has a liner 125 made of asuitable material such as a foam or gel. The patches according to thepresent invention provide for low friction support between a coveringsock or layer of material and the supporting surface. In FIG. 14, thetibial crests, the medial and lateral bony prominences near the top ofthe tibia are indicated at 130A, 126A, and 128A. The patches or pads canhave foam underneath the low friction film layer. The low frictionsurfaces reduce shear loading against the skin and subcutaneous tissuewhen the skeleton moves relative to the socket. The outer shell 124supports a lower leg portion of the prosthesis.

Additionally, the tibial crest pad 130 of FIG. 13 is aligned with thetibial crest shown at 130A in FIG. 14. The pad 130 has the PTFE filmouter layer bonded to a stretch fabric because of irregular contoursthat have to be followed on the socket. Suitable foam padding can beprovided to insure some load distribution and conformability onto thetibial crest.

Another bony area of support for a lower leg prosthesis is the fibularhead shown at 132A in FIG. 14. A fibular head pad 132 (FIG. 13) isplaced to cushion the lateral side of the remaining limb and around therear of the leg. The head of the fibula bone is quite close to the skinsurface in these locations, so that very high pressure and shear loadsare carried in this region and damage can easily occur. The patches ofthe present invention reduce the friction between the limb and thesupporting surfaces of the socket, to provide for a smooth surface thatis very low friction so that the tissue is not subjected to shearloading. The upper edges of the socket 124 can be lined with patches, ifdesired.

FIG. 15 is a view of a socket used for a full leg prosthesis(trans-femoral amputation), where support is provided at the femur andpelvic bones. The shell shown at 140 has an upper socket region 142, andthe lower portion 143 that supports a knee joint, pylon 144 and a footprosthesis 146.

In this instance, a large patch or pad 150 made according to the presentinvention can be provided in the frontal area where loads will bedirectly applied to relatively soft tissue, and this will reducefrictional loads as soft tissue tends to move, for example, the residuallimb tends to move in and out as the upper leg flexes between sittingand standing positions. the reduction in frictional loads is achieved byhaving the PTFE film layer on the exterior and the patch or pad adheredto the socket so that it does not slide on the socket. Friction loads onthe remaining limb portion is greatly reduced.

Also the patch or pad 152 avoids shear as weight is applied to thesocket, which causes relative shifting of the limb and shell.

Additionally, an irregularly shaped patch or pad 152 is provided along arear rim or edge portion loof the socket, where relatively high loadsare encountered. This pad or patch 152 can be provided with the stretchfabric layer bonded to PTFE film for conformability. A foam layer canunderlie the stretch fabric. The layer of PTFE on the exterior reducesfriction in the high load contact area between the socket supportregions and the remaining limb and pelvic bones. Other regions can alsobe covered with the pads of the present invention to provide a lowfriction interface between the remaining limb and the socket. Foamlayers can be used where needed.

A series of tests were conducted between the available products on themarket for corn pads, liners, and the like, used in shoes and otherregions where support relative to the skin is desired, as well as othermaterials, such as adhesive bandages. The following Tables 1, 2 and 3show average coefficient of friction values and standard deviations fordry and wet interface tests. Nine trials were performed for each test inmeasuring coefficient of friction, and the results averaged.

In the tests a sled surface was covered with the test material and movedacross the sock material while the force measurements were made. TABLE 1DRY TEST WET TEST Ave St Dev Ave St Dev SURFACE MATERIAL SOFT MATERIALSBockLite ⅛″ 0.49 0.10 0.56 0.03 Orthopedic Cowhide 0.49 0.11 0.68 0.03PPT with Ultrilure ® 0.57 0.07 0.57 0.02 Top Coverup IPOCON ® Gel with0.41 0.08 0.48 0.02 Lycra Top Coverup Moleskin J&J 0.63 0.03 0.87 0.03PE Lite 1/16″ 0.51 0.08 0.48 0.02 Plastazote .125″ .57 0.06 0.51 0.05Diab-A-Sheet - PPT 0.55 0.09 0.67 0.03 side up, plastazote down RussettCow Leather 0.41 0.15 0.62 0.06 PRESENT INVENTION Pad of FIG. 4 0.160.03 0.16 0.02 Pad of FIG. 2 0.16 0.01 0.17 0.01

TABLE 2 DRY TEST WET TEST Ave St Dev Ave St Dev SURFACE MATERIALBANDAGES Band-Aid ® Clear 0.47 0.01 0.53 0.01 From J & J Band-Aid ®Large 0.46 0.04 0.53 0.03 From J & J Band-Aid ® Plastic 0.45 0.02 0.510.03 From J & J Blister-Care 0.78 0.01 0.76 0.07 From Curad ® CleanSeals 0.64 0.02 0.57 0.02 From 3M Duoderm CGF 0.38 0.03 0.30 0.01 FromConvatec Nexcare Active 1.01 0.02 0.61 0.01 Strips ™ From 3M SheerBandages 0.59 0.04 0.58 0.04 From Walgreens PRESENT INVENTION Pad ofFIG. 4 0.16 0.03 0.16 0.02 Pad of FIG. 2 0.16 0.01 0.17 0.01

TABLE 3 DRY TEST WET TEST Ave St Dev Ave St Dev SURFACE MATERIALPLASTICS Orthoplast 0.29 0.02 0.46 0.09 Modified Polyethylene 0.28 0.030.30 0.03 CO Polyester 0.27 0.04 0.41 0.01 Polypropylene 0.23 0.02 0.340.05 PRESENT INVENTION Pad of FIG. 4 0.16 0.03 0.16 0.02 Pad of FIG. 20.16 0.01 0.17 0.01

In Table 1 above, Bocklite is a product manufactured by Otto BockOthopedic, Inc. Of Minneapolis, Minn.; Orthopedic Cowhide and RussettCowhide leather are available from Roden Leather of Royal Oaks Mich.;Diab-A-Sheet, a composite sheet of Plastazote and PPT foam layers andPPT with Ultrilure® top cover are both available from The LangerBiomechanics Group Inc of Deer Park, N.Y.; IPOCON® gel with Lycra topcover is sold by IPOS Orthopedics Industry, Niagara Falls N.Y.; Moleskinis an adhesive bandage sold by J.N. Johnson Sales of Minneapolis, Minn.;PE Lite and Plastazote (a polyethylene film) are sold by Pel SupplyCompany of Cleveland, Ohio.

In Table 2, all Band-Aid® products and Orthoplast are made by Johnson &Johnson Consumer Product, Inc. of Skillman, N.J.; Clean Seals andNexcare™ Active Strips™ are from 3M Health Care of St. Paul, Minn.;Blister-Care is distributed by A Beiersdorf Co. of Milford, Ohio;Duoderm CGF is distributed by the ConvaTec Division of E.R. Squibb &SSons, Inc. of Montreal, Quebec, Canada; Sheer bandages are fromWalgreens Co. of Deerfield, Ill.

In Table 3, modified Polyethylene and Co-Polyester are distributed byAmerican Plastics of Ft. Worth, Tex.; and the Polypropylene is fromSeelye Plastics, Inc. of Bloomington, Minn.

It can be seen that the pads of the present invention maintain lowerfriction characteristics whether the cotton socks used were wet or dry.For testing the “wet” socks were saturated with steam at 150° F. Some ofthe material such as BockLite did not vary substantially between wet anddry conditions (high friction in both cases), but other commonly usednatural liners such as orthopedic cowhide, moleskin, russett leather,and the like increased in coefficient of friction substantially in thepresence of moisture. The presence of moisture is common whereperspiration will cause socks to become damp.

Studies in relation to the causation of ulcers on the skin indicate thatwhen there is a relatively high level of shear, the pressure necessaryto produce blood flow occlusion is reduced substantially from whenlittle shear is present. This means that providing low friction surfacepatches in critical areas, where shear forces can be generated will tendto reduce the likelihood of formations of ulcers or calluses.

In bony areas, such as the lower leg area, shear displacements frompistoning motions result in higher shear strains where the tissue isthinnest, the shear strain is a function of the tissue thickness to thebony support. Thus, at the front edge of the leg, a similar sheardisplacement of the outer skin results in a higher shear strain than atthe rear or fleshy part of the leg. Shear strain is a function of theshear displacement divided by the thickness of tissue between thesurface of the skin and the bony support.

Thus, the present invention relates to the use of a very low frictionfilm under both dry and moist conditions, having a support surface thatsubstantially reduces the coefficient of friction that is active tocause shear loads on skin supported on that particular film, whetherthrough a sock, a cloth material of some kind, or directly against theskin. In so doing, the likelihood of ulceration, calluses, or similarproblems caused by shear strains and stresses is reduced. The size andshape of the pads can be custom made as desired, the pads can be usedwith or without foam cushioning. The pressure sensitive adhesive used isa convenient way of applying pads in regions where temporary relief maybe made, but the film can be also permanently stitched into theinterfaces of a shoe or boot, or of a prosthetic device, such as aprosthetic limb. Installation of pads in orthoses is also veryconvenient. Treatment can be carried out for spots that seem to bedeveloping sores or which become tender, by placing a low friction patchbetween the load bearing area of the body or skin and the object that isapplying the load so that shear is reduced in that localized area. Thus,the method of treatment includes adding suitable sized patches inregions between tender or sole areas of the skin and the shoe or supportobject.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A patch for reducing friction between portions of the skin of aperson and an object supporting that portion of the skin comprising apatch having a layer of film with an exterior surface having acoefficient of friction substantially equal to that ofpolytetrafluoroethylene, and a securing member for securing the filminto position on one of the object and skin.
 2. The patch of claim 1,wherein the securing member comprises a layer of pressure sensitiveadhesive on one side of the patch.
 3. The patch of claim 1 including abonded stretch fabric on one side of the film opposite from the exteriorsurface, said exterior surface providing an interface surface betweenthe portion of the skin and the object.
 4. The patch of claim 1including a layer of a foam material on a side of said film oppositefrom the exterior surface.
 5. The patch of claim 2 and a release paperon the exterior of the adhesive layer.
 6. The patch of claim 1 includinga plurality of backing layers for the film including a stretch fabricbonded to the film on one surface thereof, a foam layer in a selectedregion of the patch secured to the fabric, and a pressure sensitiveadhesive on at least portions of the patch opposite from the exteriorsurface for forming the securing member.
 7. The patch of claim 6,wherein said patch has an exposed portion of pressure sensitive adhesivesurrounding a center portion, the foam layer being exposed in the centerportion for application to one of the object and the skin.
 8. The patchof claim 1 including a layer of low friction material on a surface ofthe patch opposite from the exterior surface.
 9. The patch of claim 1including a foam layer between the layer of film and the one of theobject and skin.
 10. The patch of claim 2, wherein the patch has aplurality of perforations therethrough.
 11. The patch of claim 1,wherein the patch is formed with a periphery that is oval.
 12. The patchof claim 1, wherein the patch is formed with a rectilinear periphery.13. A friction management method for a support object supporting aportion of a human body having support bones, tissue around the supportbones and skin on an outer side of the tissue, including selectingpressure regions of high loads when load is carried between the objectand the human body supported, applying selected patches of materialhaving low friction surfaces interfaced between the object and the skinin the selected regions.
 14. The friction management method of claim 13,wherein the object comprises a shoe, and the selected regions includethe metatarsal-phalangeal joint region.
 15. The friction managementmethod of claim 14, wherein the calcaneus region comprises the regionsupported on low friction surface patches.
 16. The friction managementmethod of claim 13, wherein the object comprises a prosthetic devicehaving a socket for receiving a portion of a limb to be supported, andproviding patches at specific high load locations between an interiorsurface of the socket and a supported limb.
 17. A method of reducingtrauma to tissue supported on an object including steps of selecting aplurality of support regions of high load where shear load on tissue islikely to cause damage, and providing a low friction surface patchbetween each of the plurality of the regions of high load and an objectsupporting the tissue.
 18. The method of claim 17, including a step ofselecting the low friction material to have a coefficient of frictionsubstantially equal to that of polytetrafluoroethylene.
 19. The methodof claim 17, wherein the selecting step includes identifying supportregions where low friction surface patches are omitted.
 20. The methodof claim 17 including the step of providing a patch having a lowcoefficient of friction material exposed on oppositely facing supportsurfaces of the patch.